iBooks: It wasn't just third party apps available with iOS4, the iBooks app for the iPhone was just released on the app store as well. It syncs page number, bookmarks, and notes between the iPhone and iPad.

Windows Messenger: A new app and it comes out with iOS4 integration built-in. It also supports alerts for Hotmail as well, so you’ll get notifications in-app when you receive new e-mails via your Hotmail account.